Alginate and galactomannan-derived oligosaccharides enhanced the production of penicillin G when added to stirred tank reactor cultures of Penicillium chrysogenum. The addition of oligomannuronate and oligoguluronate blocks increased penicillin G yield by 47% and 49%, respectively. The effect of mannan oligosaccharides was found to be more pronounced with 69% higher yield than the control cultures. The maximum increase in the average specific productivity of the oligosaccharide augmented cultures was 55% after addition of mannan oligosaccharides. In addition, a difference was observed in all cases in the accumulation pattern of the intermediate of penicillin biosynthesis, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine.